The present invention relates to an electric rotary machinery, for example, a water-wheel generator-motor, of salient-pole type, in which ventilation cooling is employed.
The electric rotary machinery of salient-pole type such as water-wheel generator-motor has become larger and larger in capacity these days, and particularly the water-wheel generator-motor has the most remarkable tendency of its becoming higher in speed and larger in capacity so as to reduce the building cost of a power plant. In the case of this large-sized generator-motor, however, it is difficult that the amount of cooling air necessary to cool the generator-motor is obtained overcoming the flow resistance in a ventilating passage on the side of a stator, when only the centrifugal fan effect thanks to the rotation of a salient-pole type rotor is used. Therefore, ventilating ducts are arranged in a rotor rim to further enhance the centrifugal fan effect due to the rotor, or electric fans are additionally arranged to compensate the lack of cooling air.
FIG. 1 is a longitudinally-sectional view showing the ventilation cooling arrangement of a conventional vertical type generator-motor 10. A plurality of salient-poles or magnetic poles 16 are fixed on the outer circumference of a rotor rim 14 attached to a rotary shaft 12 of generator-motor 10, and cooling air or wind caused by the centrifugal fan effect due to the rotation of magnetic poles 16 axially enters into spaces 17 between magnetic poles 16, radially flows through stator air ducts 20 in a core 18 of a stator 42, cooling the stator core 18 and a stator coil 18a, then through an air cooler 24 attached to the outer circumference of a stator frame 22 into a space or outer circumferential air passage 10a between the generator-motor 10 and a pit wall 32, and finally enters as again-cooled air or wind into spaces 17 between magnetic poles 16. Cooling air or wind is thus circulated through the above-described passage or air circulating passage.
In the case where the cooling effect attained according to the above-described cooling system was not enough, rotor air ducts 26 were arranged in the rotor rim 14 to enhance the fan effect of rotor 28, and electric fans 30 were further added when it was thought necessary to increase the amount of cooling air or wind.
FIG. 2 is a graph showing the pressure-flow rate characteristic of cooling system attained by the generator-motor 10 shown in FIG. 1. The axis of abscissa represents the flow rate of cooling air when it is converted to one barometric pressure. The vertical axis of coordinates represents the difference between the pressure P of cooling air or pressure generated when the rotor is regarded as a blower, i.e. pressure just before air ducts 20 of stator core 18 and the pressure enclosing the rotor 28.
Curve Z in the graph represents the relation between the pressure applied to the flowing passage of cooling air and the flow rate and can be regarded as representing the flow resistance in the flowing passage. The flow resistance is determined by both the ventilation resistance in the air cooler 24 and the loss of air when it is curved flowing from the air cooler and entering into the inlet of rotor 28. A curve A is one of pressure-flow rate curves which show the characteristic of fan effect attained thanks to the projected pole of rotor 28. Curve A shows the most fundamental characteristic in the case where no rotor air duct 26 is provided in the rotor rim 14 and cooling air axially flows through spaces 17 between magnetic poles while radially flowing toward the stator core 18.
A point Pa where curves A and Z intersect denotes the working point of ventilating function attained by the salient poles. The flow rate is represented by Q.sub.0 at this time. A curve B represents the relation between pressure and flow rate in a case where rotor air ducts 26 are provided in the rotor rim 14. The fan effect of rotor 28 is enhanced thanks to the presence of rotor air ducts 26 and a point Pb where curves B and Z intersect denotes the working point of ventilating function. The flow rate at the point Pb becomes equal to Q.sub.1 which is larger than Q.sub.0. A curve C represents the relation between pressure and flow rate in a case where an optional number of electric fans are arranged in addition to rotor air ducts 26 to increase the flow rate of cooling air, and a point Pc where curves C and Z intersect becomes the working point of ventilating function. The flow rate at this point becomes equal to Q.sub.2 which is larger than Q.sub.1.
Assuming that the desired flow rate is Q.sub.2, power necessary to flow cooling air of flow rate Q.sub.2 through the generator-motor which has characteristics represented by curves A and B will be calculated.
It can be found from FIG. 2 that the pressure which electric fans must bear to flow cooling air of flow rate Q.sub.2 through the generator motor 10 which is provided with rotor air ducts 26 is Pf.sub.2. It can be therefore understood that the power Lf.sub.2 necessary to drive electric fans is denoted by the following equation: ##EQU1## where .eta. represents the efficiency of electric fans.
Similarly as apparent from FIG. 2, it can be understood that the pressure which electric fans must bear to flow cooling air of flow rate Q.sub.2 through the generator motor 10 which has no rotor air duct 26 is Pf.sub.1 and that the power Lf.sub.1 necessary to drive electric fans is denoted by the following equation: ##EQU2##
When these relations are considered with reference to FIG. 2, Pf.sub.2 &lt;Pf.sub.1. Therefore, the larger flow rate Q.sub.2 seems to naturally be obtained by smaller power when as many rotor air ducts 26 as possible are arranged to enhance the fan effect of rotor 28 and a further lack of flow rate is added by electric fans 30. Accordingly, the capacity of electric fans was conventionally determined according to this manner of consideration.